Kinetic Modeling of Langmuir Probes in Space and Application to the MAVEN Langmuir Probe and Waves Instrument

Abstract

AbstractSelf‐consistent kinetic solutions from test‐particle simulations are used to improve the derivation of electron temperature (Te) and density (ne) from Langmuir probes in space. While Langmuir probes are well understood, the non‐ideal characteristics of space‐flight instruments can influence the accuracy of Te and ne and how they are derived. In particular, when in an ionosphere, spacecraft motion often causes a sensor wake and exposes its surface to oxidation. This work has two primary goals. We present kinetic solutions of general interest then apply our findings to the Langmuir Probe and Waves (LPW) instrument on the MAVEN satellite. Of general interest, (1) kinetic solutions show that mechanical mounting of a Langmuir probe sensor and controlling the potential of nearby surfaces is critical for accuracy. (2) An ion wake generated by the sensor can greatly modify how ne must be derived. (3) Interestingly, small voltage variations on the surface of the sensor do not significantly diminish the accuracy of Te and ne. (4) On the other hand, surface resistance on the sensor can appreciably disturb the derivation of Te. The LPW instrument is recalibrated with the aid of kinetic solutions and published results from laboratory experiments. The systematic uncertainty (as opposed to random variations) in Te is improved to as low as ±0.005 eV (±60 K) when ne > ∼3 × 104 cm−3. This recalibration leads to some of the most accurate measurements of Te made in space and can result in improved modeling of Mars' ionosphere.